Herschel Space Observatory Calibration Workshop: Models and Observations of astronomical calibration sources 1-3 December 2004, Leiden, The Netherlands SolidSolid StateState FeaturesFeatures inin thethe FarFar--InfraredInfrared

Franz Kerschbaum, Thomas Posch (Vienna) & Harald Mutschke (Jena)

ISOISO’’ss AstromineralogyAstromineralogy LegacyLegacy z ISO caused a revolution in the field of astromineralogy in all dusty environments from the earliest to the latest stages of stellar evolution (for an overview, see Henning 2003) z But most of these findings Sylvester et al. (1999) were in the SWS- and not the Posch et al. (2002) LWS-range! LWS-range! 1.1 Mg Fe O em. 0.1 0.9 z Herschel-PACS operational in the g Her (1) 2

λ 1.0 g Her (2) * 57-210µm range with unprece- ν V1943 Sgr dented sensitivity and spatial 0.9 resp. F

resolution - What can we expect? abs 0.8 Q

0.7 14 16 18 20 22 24 λ (µm) 2 SomeSome basicbasic physicsphysics

Principal mechanisms for emission in the 57µm+ range:

1. Lattice vibrations of heavy ions and/or ion groups with low bond energies

z Example KBr is highly transparent in the NIR and MIR (matrix material for transmission spectroscopy!) but opaque in the FIR (transverse optical mode at 86µm). NaCl and KCl are similar cases (61 and 69µm, respectively) z This can be understood by a harm. oscillator law (e.g. Beran et al. 2004): µ λ ∝ vib k with µ being the reduced mass and k the force constant. z Limited range of mass numbers of dust forming elements

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SomeSome basicbasic physicsphysics

Principal mechanisms for emission in the 57µm+ range:

2. Phonon-difference processes

z Phonon-difference processes mainly contribute to the continuum emissivity (e.g. Mitra & Nudelmam 1970)

z No well defined individual bands expected

z Nevertheless their contribution to the continuum may partly mask FIR bands

4 ComparisonComparison ofof grainsgrains (Jones 2004)

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DustDust compositioncomposition asas aa functionfunction ofof MLRMLR

6 ForsteriteForsterite z Crystalline silicates initially identified by Forsterite Waelkens et al. (1996) on basis of ISO- 10K Mg SiO SWS observations and subsequently also 2 4 in ISO-LWS spectra) with forsterite’s 0.9 69µm band (Malfait et al. 1998) 40K z Bowey et al. (2002) showed that the

69µm band strongly sharpens at low 200K temperatures in parallel to a shift in peak position (for 295, 77 and 3.5K) 0.8 z We complement these results by Transmittance measurements at 300, 200, 40 and 10K 300K z Respective transmittance spectra show a shift of the band position from 69.7 to

68.7µm, consistent with Bowey et al. 68.7µm 69.7µm

See also Koike et al. 66 68 70 72 74 and Suto et al. (2004) λ / µm Powder pellet, sample thickness 0.8mm Bowey et al. (2002)

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FayaliteFayalite

Fayalite z Iron-rich endmember of olivine group Fe SiO 2 4 40K 0.2 z Hofmeister (1997): at least two vib. bands in Herschel-PACS range centered at 94 and 110µm with the latter seen in powder transmission 0.2 spectra only if sample thickness and 200K S/N ratio are sufficient 0.1 z New measurements of both bands at low temperatures (T=200K for the 93- Transmittance 94 µm band, T=40K for the 110µm 300K 94 µm band, T=40K for the 110µm 0.1 band needed). z For the 93-94µm band: significant 110.3µm

sharpening as sample cools down 0.0 93.0µm z T-dependence of position: 93.0µm at

200K, 92.9µm at 40K and 92.6µm 90 100 110 120 130

at 10K λ / µm z Mutschke et al. (2004) will present a detailed analysis of olivines at low T! Powder pellet, sample thickness 0.8mm

8 DiopsideDiopside z Koike et al. (2000): crystalline diopside has a peak wavelength of lowest energy vib. band at 65- 66µm. Peak not present in amorphous diopside! z Compared to the 60+µm bands of crystalline orthoenstatite, clinoenstatite and orthopyroxene, its 65-66µm band is much stronger z Found in planetary nebulae (Koike et al. 2000, Kemper et al. 2002) z SF-regions such as the Carina and S171 also exhibit a 65-66µm emission feature NGC6302, Kemper et al. (2002) attributable to crystalline CaMgSi2O6 (Onaka & Okada 2003)

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OtherOther SilicatesSilicates

There do exist others silicate of astrophysical relevance with signatures in the 60+µm range:

z Malfait et al. (1999) consider montmorillonite - a hydrous silicate containing Ca, Na, Al, Mg and Fe - as carrier of a broad band centered at 100-110µm, detectable in the spectrum of the young HD 142527!

• Gehlenite (Ca2Al2SiO7):) broad band at 66µm

z Fassaite ((Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6): band at 62µm (Keller & Flynn 2003, LPI Conf. Abstr. 34, 1903)

10 CarbonatesCarbonates z Several carbonates have features of considerable strength in the 60+µm range (e.g. Kemper et al. 2002) z These resonance features are not related to C-O stretching or bending modes, but to translations of metal cations (Ca, Mg, Fe) relative to the plane of the CO3 anions following our earlier ‘weak bond strength argument’ z Typical examples are: Calcite (CaCO3) at 92µm Dolomite (CaMg(CO3)2) at 62µm NGC6302, Kemper et al. (2002)

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GraphiteGraphite z Hexagonal polymorph of carbon z Sharp features in the MIR and a broad band at 50-70µm z Draine & Lee (1984) pointed out that: z exact position of this broad band depends both on grain size and grain temperature z Grain sizes < 1µm: maximum of absorption efficiency at 50µm z Grain size of 1µm: maximum is shifted to 70µm z At low temperatures (100K), the width of the band is reduced from 100µm to 70µm! z Electronic origin of the feature (inter-band transition) z Even when broad and weak it may contribute to the uncertainty of the continuum!

12 WaterWater iceice z ice has quite significant FIR-features! Frosty in I,J, H z The 44-46µm band is present both in amorphous Roddier et al. (1993) and crystalline (hexagonal) water ice, the 62µm- band only in crystalline H2O ice z At 120-130K: phase transition from the amorphous state (extremely low temperatures) to the crystalline state (at intermediate temperatures) z The 44-46µm band shifts in position at this transition (~46 → ~44µm), the 62µm band emerges → The 62µm band is an ideal diagnostic tool for the lattice structure of H2O in cosmic dust (see e.g., Maldoni et al. 1999 and references therein) z The 62µm feature originates in the longit. acoustic mode of crystalline H2O; the 44-46µm feature is the transverse optical mode 13

WaterWater iceice z Environments in which the 62µm water ice feature is detected: Frosty Leo in I,J, H Roddier et al. (1993)

z Omont et al. (1990): IRAS 09371+1212 (Frosty Leo nebula), a post-AGB star with extremely cold dust (see Barlow et al. (1998) for more post-AGB ) z Kemper et al. (2002) found water ice (1%) in the PN NGC 6302 z Malfait et al. (1999) detected it in some Herbig Ae/Be stars z Molinari (1999) detected it in the Herbig-Haro object HH 7

14 OtherOther icesices z Methanol ice (α-CH3OH ): according to Moore & Hudson (1994), amorphous form shows broad band 67.7µm (at 13K), while crystalline methanol ice has bands at 68.0 and 88.5µm z Dry ice (CO2): Amorphous phase shows a rather sharp feature located at 85.5µm (at 13K); the crystalline form has an even Amorphous mixtures [+annealed] sharper ~85µm band with a quite strong T-dependence of the band position (40K and below: 88.5µm; 85K: 85.5µm) (Moore & Hudson 1994) z Considering both the temperature dependences and the likelihood of mixtures of different ice species in space (formation of core-mantle-grains!), a lot of laboratory work remains to be done in this field!

Crystalline forms 15

SelectedSelected dustdust andand iceice speciesspecies withwith bandsbands inin thethe 60+60+µµmm rangerange Mineral chemical formula band positions [µm] ref. (at λ > 60µm)

Forsterite Mg2SiO4 69-70 [1]

Fayalite Fe2SiO4 93-94, 110 [1]

Diopside CaMgSi2O6 65-66 [2]

Calcite CaCO3 92 [3]

Dolomite CaMg(CO3)2 62 [3] Graphite C 50-70 [4]

Water ice H2O 62 [5]

Methanol ice α-CH3OH 68, 88.5 [6]

Dry ice CO2 85 [6]

[1] Posch et al. (2004), [2] Koike et al. (2000), [3] Kemper et al. (2000), [4] Draine & Lee (1984), [5] Maldoni et al. (1999), [6] Moore & Hudson (1994)

16 DustDust EvolutionEvolution

• Photo-processing • Photo-destruction • Amorphization (cosmic rays) • Grain shattering/sputtering in supernovae shocks or turbulent clouds • Grain coagulation Jones (2004) •…

Subsequent changes in optical properties need to be studied in the laboratory in much more detail!

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JenaJena--DatabaseDatabase ofof opticaloptical constantsconstants ofof astronomicallyastronomically relevantrelevant solidssolids

z The Jena-database already provides the refractive index n(λ) and the absorption index k(λ) of a large number of silicates, oxides, sulfides and carbon materials from own laboratory measurements: http://www.astro.uni-jena.de/Laboratory/Database/databases.html

z A visualisation of n(λ), k(λ) and the absorption efficiency (Qabs/a) linked to the database is currently in preparation

18 SomeSome selectedselected otherother databasesdatabases

z St. Petersburg database: http://www.astro.spbu.ru/JPDOC z B.T. Draine’s page: http://www.astro.princeton.edu/~draine/dust/ z Astrobiology Group, Leiden: http://www.astrobiology.nl/isodb/index.html z ASTER spectral library, JPL: http://speclib.jpl.nasa.gov/ z Crystran Ltd, Dorset, UK http://www.crystran.co.uk

Two printed classic atlases unfortunately only out to 25 µm: z Salisbury J.W., Walter L.S., Vergo N, D'Aria D.M. (1991), Infrared (2.1 – 25µm) Spectra of Minerals, J.Hopkins University Press, Baltimore z H. Moenke (1962), Mineral Spektren, I, Akademie-Verlag, Berlin

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SummarySummary

z In general the 57µm+ range is not as rich in vibrational bands as the MIR range is z This is due to the typical masses and force constants of the relevant ions and group of ions in cosmically abundant solids z The 57µm+ range contains some features that can serve as indicators of local physical/chemical conditions (e.g. 69µm forsterite or 62µm water ice) z Further lab work should concentrate e.g. on the T-dependence of FIR spectra including very low temperatures

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